Fault tolerant control of a terminal unit in a climate control system

ABSTRACT

A method for controlling a terminal unit in a climate control system includes detecting a stuck position of a first actuator in the terminal unit; receiving a command signal identifying a commanded capacity; and controlling a second actuator in the terminal unit in response to the stuck position of the first actuator and the commanded capacity.

BACKGROUND

Embodiments relate generally to climate control systems, and more particularly to fault tolerant control of a terminal unit in a climate control system.

Existing climate control systems include a number of terminal units to condition air supplied to spaces associated with the terminal units. At each terminal unit, one or more actuators may be used to control the capacity of the terminal unit. For example, a first actuator (e.g., a valve) may be used to control the flow of conditioned fluid through a coil in the terminal unit and a second actuator (e.g., a fan motor) may be used to move air over the coil and to a space to be conditioned. If one actuator, e.g., the valve, remains stuck fully or partially open, the capacity transmitted can be significantly more than what was intended with the command input sent to the terminal unit (i.e., terminal unit output capacity is not the same as commanded input). This results in poor comfort for occupants as the control of the room temperature can be quite off, leading to excess heating (or cooling), and poorly or hardly ever stabilizing to the desired temperature. The actuator fault also results in excessive energy consumption. For example, when the valve is stuck partially open, regardless of whether comfort is achieved or not, excess demand is expected from heat pump/chiller which is otherwise not required.

SUMMARY

According to one embodiment, a method for controlling a terminal unit in a climate control system includes detecting a stuck position of a first actuator in the terminal unit; receiving a command signal identifying a commanded capacity; and controlling a second actuator in the terminal unit in response to the stuck position of the first actuator and the commanded capacity.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein controlling the second actuator includes: accessing an adaptive coordination map, the adaptive coordination map associating the commanded capacity with a second actuator drive signal for the stuck position of the first actuator; and applying the second actuator drive signal to the second actuator.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein controlling the second actuator includes: computing a second actuator drive signal in response to the commanded capacity and the stuck position of the first actuator; and applying the second actuator drive signal to the second actuator.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein the detecting the stuck position of the first actuator in the terminal unit includes providing a range of drive signals to the first actuator; and determining if the first actuator responds to the range of drive signals.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein determining if the first actuator responds to the range of drive signals includes sensing movement of the first actuator.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein determining if the first actuator responds to the range of drive signals includes sensing fluid flow or temperature in the terminal unit.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein determining if the first actuator responds to the range of drive signals includes determining an output capacity of the terminal unit.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein determining the output capacity of the terminal unit includes sensing discharge air temperature of the terminal unit.

According to another embodiment, a terminal unit system includes a controller; and a terminal unit having an actuator; the controller configured to control the actuator, the controller configured to perform operations including detecting a stuck position of a first actuator in the terminal unit; receiving a command signal identifying a commanded capacity; and controlling a second actuator in the terminal unit in response to the stuck position of the first actuator and the commanded capacity.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein controlling the second actuator includes accessing an adaptive coordination map, the adaptive coordination map associating the commanded capacity with a second actuator drive signal for the stuck position of the first actuator; and applying the second actuator drive signal to the second actuator.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein controlling the second actuator includes computing a second actuator drive signal in response to the commanded capacity and the stuck position of the first actuator; and applying the second actuator drive signal to the second actuator.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein the detecting the stuck position of the first actuator in the terminal unit includes providing a range of drive signals to the first actuator; and determining if the first actuator responds to the range of drive signals.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein determining if the first actuator responds to the range of drive signals includes sensing movement of the first actuator.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein determining if the first actuator responds to the range of drive signals includes sensing fluid flow or temperature in the terminal unit.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein determining if the first actuator responds to the range of drive signals includes determining an output capacity of the terminal unit.

In addition to one or more of the features described above, or as an alternative, further embodiments may include wherein determining the output capacity of the terminal unit includes sensing discharge air temperature of the terminal unit.

Technical effects of embodiments of the disclosure include the ability to detect stuck actuator(s) and control other actuator(s) so that output capacity of the terminal unit matches a commanded capacity.

These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter is particularly pointed out and distinctly claimed at the conclusion of the specification. The foregoing and other features, and advantages of the present disclosure are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 depicts a climate control system in an exemplary embodiment;

FIG. 2 depicts a terminal unit in an exemplary embodiment;

FIG. 3 depicts a flowchart of a process for controlling a terminal unit in an exemplary embodiment; and

FIG. 4 depicts an adaptive coordination map in an exemplary embodiment.

The detailed description explains embodiments, together with advantages and features, by way of example with reference to the drawings.

DETAILED DESCRIPTION

FIG. 1 depicts a climate control system 10 in an exemplary embodiment. The climate control system 10 includes a conditioning system 12 and a terminal unit system 14. The conditioning system 12 includes a compressor 18, first heat exchanger 20 (e.g., condenser/gas cooler), an expansion valve 22 and a second heat exchanger 24 (e.g., an evaporator). In operation in a cooling mode, gaseous refrigerant is induced into compressor 18 and compressed. After the refrigerant is compressed, the high temperature, high pressure refrigerant gas is supplied to condenser 20. In condenser 20, the gaseous refrigerant condenses into liquid as it gives up heat to another fluid (e.g., air). The liquid refrigerant passes through expansion valve 22 to reduce pressure and then flows to evaporator 24. In the evaporator 24, the refrigerant changes state to a gas and absorbs heat from a fluid (e.g., water) passing through evaporator 24. The fluid is circulated in the terminal unit system 14 as described in further detail herein. The low pressure vapor is then drawn into the inlet of compressor 18 and the cycle is continually repeated.

Although the conditioning system 12 is shown as cooling fluid circulated in the terminal unit system 14, the conditioning system 12 may also heat fluid circulated in the terminal unit system 14. A reversing valve may be used to reverse the flow of refrigerant in the conditioning system such that heat exchanger 24 heats fluid circulated in the terminal unit system 14. The conditioning system 12 is not limited to using refrigerant compression systems, but may utilize other techniques (e.g., free cooling, thermoelectric, gas boiler, etc.) to condition fluid circulated in the terminal unit system 14.

The terminal unit system 14 includes a plurality of terminal units 30, each of which supplies conditioned air to a space, such as a building floor, room, etc. Each terminal unit 30 may serve a separate space, or multiple terminal units 30 may supply a single space. Fluid is circulated to and from the terminal units 30 by one or more pumps 32. An air handler 34 provides supply air to each terminal unit 30. As known in the art, the air handler 34 receives return air (a portion or all of which may be expelled as exhaust air) and outside air to form the supply air stream. Each terminal unit 30 includes a coil that receives fluid from pump(s) 32 at a coil inlet 46 and expels fluid at a coil outlet 48. Fluid from the coil outlets 48 is returned to the heat exchanger 24 for conditioning. Supply air flows over the coils to provide a conditioned supply air to each space.

A supervisory controller 40 may communicate with each terminal unit 30 and send command signals to each terminal unit 30. The command signals may command operation of one or more actuators at each terminal unit 30 to achieve a desired capacity (e.g., heating or cooling) at each terminal unit 30. The command signal may refer to a desired output capacity for the terminal unit 30 (e.g., 30% of maximum capacity). The supervisory controller 40 may include a processor and an associated memory. The processor may be but is not limited to a single-processor or multi-processor system of any of a wide array of possible architectures, including field programmable gate array (FPGA), central processing unit (CPU), application specific integrated circuits (ASIC) or digital signal processor (DSP) hardware arranged homogenously or heterogeneously. The memory may be, but is not limited to, a random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic or any other computer readable medium.

In operation, fluid in the terminal unit system 14 is conditioned (e.g., cooled or heated) at the heat exchanger 24. The pump(s) 32 circulate(s) the fluid to the coils at coil inlets 46. Supply air from the air handler 34 passes over the coils to provide conditioned air to the respective spaces. Once the fluid passes through a coil, it emerges at the coil outlet 48 and is returned to the heat exchanger 24 for further conditioning. Again, FIG. 1 is one example of a climate control system, and a variety of architectures may be used in embodiments of the disclosure.

FIG. 2 depicts a terminal unit 30 in an exemplary embodiment. The terminal unit 30 includes a coil 52. As noted above, supply air passes over coil 52 to provide conditioned air to the space. Flow of conditioned fluid through coil 52 is controlled by a first actuator 54, which may be an electronically controlled valve. Airflow through the terminal unit 30 may be controlled by one or more additional actuators. A second actuator 56 may be a fan motor, and can be controlled to increase or decrease air flow through terminal unit 30. A third actuator 58 may be a damper actuator, and can be controlled to move a damper to increase or decrease air flow through terminal unit 30. Actuators 54, 56 and 58 are exemplary only, and embodiments may use one or more different actuators, alone or in combination, to control capacity of the terminal unit 30.

A terminal unit controller 60 is coupled to the first actuator 54, second actuator 56 and third actuator 58. The terminal unit controller 60 is also coupled to one or more sensors 62 that provide an indication of capacity of the terminal unit 30. The terminal unit controller 60 may include a processor and an associated memory. The processor may be but is not limited to a single-processor or multi-processor system of any of a wide array of possible architectures, including field programmable gate array (FPGA), central processing unit (CPU), application specific integrated circuits (ASIC) or digital signal processor (DSP) hardware arranged homogenously or heterogeneously. The memory may be, but is not limited to, a random access memory (RAM), read only memory (ROM), or other electronic, optical, magnetic or any other computer readable medium.

In operation, the terminal unit controller 60 receives command signals from the supervisory controller 40 and generates one or more drive signals that are applied to each actuator. A command signal may, for example, be a digital signal that specifies a capacity (e.g., a percentage of maximum capacity). A drive signal may, for example, be an analog voltage applied to each respective actuator. As noted above, if one of the actuators 54, 56 and 58 is stuck in a fixed position, the output capacity of the terminal unit 30 may not match the capacity identified in the command signal. Embodiments of the disclosure detect one or more stuck actuators and control the other actuators so that the output capacity of the terminal unit 30 matches the commanded capacity.

FIG. 3 depicts a flowchart of a process for detecting a stuck actuator in a terminal unit 30 and controlling the remaining actuators in response to detecting a stuck actuator. It is understood that more than one stuck actuator may be detected, and embodiments are not limited to operation with only one stuck actuator. The process may be implemented by the terminal unit controller 60, the supervisory controller 40, or both controllers operating in conjunction. In the described embodiment, the terminal unit controller 60 performs the process of FIG. 3. The process begins at 200 where the terminal unit controller 60 detects if an actuator is stuck and, if so, the stuck position. Step 200 may be performed periodically (e.g., once daily, weekly, monthly, etc.) at periods where occupants are not expected to present in the space. Detecting a stuck actuator may be performed in a variety of ways. In one embodiment, the actuators 54, 56 and 58 may each include an encoder in communication with the terminal unit controller 60. The terminal unit controller 60 sends a range of drive signals (e.g., 0% to 100%) to an actuator and confirms that the actuator is responding by monitoring the encoder output. This may be done individually for each actuator. The encoder output is indicative of movement of the actuator. The encoder output is also indicative of the current position of the actuator if the actuator is stuck.

In other embodiments, sensors located in the terminal unit 30 are used to determine if an actuator is stuck. For example, a flow meter may be placed in the fluid path including valve 54. The terminal unit controller 60 sends a range of drive signals (e.g., 0% to 100%) to valve 54 and monitors the flow meter to confirm that fluid flow through the valve 54 changes with the changing drive signals. A flow meter may also be placed in the airstream to confirm that air flow provided by fan motor 56 changes with the changing drive signals. If the sensor reading does not change with changing drive signals, the stuck position can be determined from the sensed value. For example, if a flow meter indicates a constant 50% fluid flow rate through valve 54, then valve 54 may be determined to be stuck at a 50% opening. In other embodiments, a temperature sensor may be used to sense if temperature(s) in the terminal unit are changing over the range of drive signals provided to the actuator.

In another embodiment, the output capacity of the terminal unit 30 is monitored as each actuator is individually adjusted. For example, the discharge air temperature at the terminal unit 30 may be measured by sensor 62 while the terminal unit controller 60 sends a range of drive signals (e.g., 0% to 100%) to each actuator, individually. For example, as the valve 54 is moved from fully closed to fully open, the discharge air temperature should decrease (in a cooling mode) with the increasing valve 54 opening. If the output capacity of the terminal unit 30 does not change with changes to actuator position, then the terminal unit controller 60 determines the actuator is stuck. The terminal unit controller 60 can use a priori information about the terminal unit 30 to determine at what position the actuator is stuck. For example, the expected output capacity of the terminal unit 30 may be known for various combinations of positions of actuators 54, 56, and 58. The terminal unit controller 60 can detect the stuck position of an actuator based on the output capacity of the terminal unit 30 using this a priori information. For example, varying actuators 56 and 58 may indicate that actuator 54 is stuck at a 50% position based on the output capacity of the terminal unit 30.

If at 200 no actuator is stuck, the terminal unit system 14 operates under normal conditions as shown at 201. If at 200 an actuator is found to be stuck, flow proceeds to 202 where the terminal unit controller 60 obtains a command signal identifying a commanded capacity. The command signal maybe provided by the supervisory controller 40 or generated by the terminal unit controller 60. At 204, in order to meet the commanded capacity, the terminal unit controller 60 adjusts the drive signal(s) to the other actuator(s) to compensate for the stuck position of the stuck actuator.

At 204, the drive signal(s) for the other actuator(s) may be derived in a variety of ways. FIG. 4 depicts an adaptive coordination map that may be used by terminal unit controller 60 to determine a drive signal for a second actuator in response to a stuck position of a first actuator. The adaptive coordination map may be stored as a look-up table in terminal control unit 60. In the example of FIG. 4, the stuck actuator is valve 54 and the second actuator is fan motor 56. The adaptive coordination map shows a baseline plot 400 of fan speed when no actuator(s) are stuck. The adaptive coordination map also depicts plots of fan speed versus commanded capacity for various stuck positions of valve 54. Plot 402 corresponds to valve 54 stuck 100% open, plot 404 corresponds to valve 54 stuck 90% open and plot 406 corresponds to valve 54 stuck 30% open. It is understood that a complete adaptive coordination map may include a higher number of stuck actuator positions. The terminal unit controller 60 obtains the commanded capacity and, based on the stuck position of valve 54, obtains the fan speed command which is used for the drive signal applied to the fan motor 56. For example, for valve 54 stuck open at 90%, a commanded capacity of 70% will result in a fan speed of about 45%. While the adaptive coordination map of FIG. 4 relates fan speed to valve stuck position, it is understood that multiple adaptive coordination maps may be used, relating one or more stuck actuator positions to multiple drive signals.

In another embodiment, the drive signal(s) for the unstuck actuator(s) may be computed by the terminal unit controller 60 based on the commanded capacity and the stuck position of an actuator. In the example of stuck valve 54, the commanded capacity may be, for example, 60%. As the valve 54 is stuck at, for example 40%, there is a 20% difference between the commanded capacity and the stuck position. To accommodate for this difference, the fan speed drive signal may be adjusted in proportion to this difference. The fan speed may be increased by 20% (or some proportion of 20%) to accommodate for the valve 54 being stuck at a level below the commanded capacity. A negative difference (e.g., commanded capacity is less than stuck position) may also be used to reduce the fan speed in proportion to this difference. While the above example relates fan speed to valve stuck position, it is understood that multiple calculations may be used, relating one or more stuck actuator positions to multiple drive signals.

Once the drive signal(s) for the unstuck actuator(s) are obtained at 204, flow proceeds to 208 where the terminal unit controller 60 applies the drive signal(s) to the unstuck actuator(s). The process continues until the stuck actuator(s) can be repaired, at which time the normal operations can resume.

In another embodiment, some or all of the processes previously described and executed at the terminal unit controller 60 might instead be executed at the supervisory controller 40, and this for one or several terminal units.

Embodiments compensate for one or more stuck actuators by adjusting drive signals to other actuators in response to a commanded capacity and the stuck position of the actuator(s). This allows the system to provide accurate room temperature control (i.e., improved comfort) even in the presence of stuck actuator. Embodiments also reduce excess energy consumption in the presence of stuck actuator. The stuck actuator is tolerated without any manual intervention and therefore, provides more time for the technician to fix the fault.

While the disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the scope of the invention. Additionally, while various embodiments have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims. 

What is claimed is:
 1. A method for controlling a terminal unit in a climate control system, the method comprising: detecting a stuck position of a first actuator in the terminal unit; receiving a command signal identifying a commanded capacity; and controlling a second actuator in the terminal unit in response to the stuck position of the first actuator and the commanded capacity.
 2. The method of claim 1 wherein: controlling the second actuator comprises: accessing an adaptive coordination map, the adaptive coordination map associating the commanded capacity with a second actuator drive signal for the stuck position of the first actuator; and applying the second actuator drive signal to the second actuator.
 3. The method of claim 1 wherein: controlling the second actuator comprises: computing a second actuator drive signal in response to the commanded capacity and the stuck position of the first actuator; and applying the second actuator drive signal to the second actuator.
 4. The method of claim 1 wherein: the detecting the stuck position of the first actuator in the terminal unit includes providing a range of drive signals to the first actuator; and determining if the first actuator responds to the range of drive signals.
 5. The method of claim 4 wherein: determining if the first actuator responds to the range of drive signals includes sensing movement of the first actuator.
 6. The method of claim 4 wherein: determining if the first actuator responds to the range of drive signals includes sensing fluid flow or temperature in the terminal unit.
 7. The method of claim 4 wherein: determining if the first actuator responds to the range of drive signals includes determining an output capacity of the terminal unit.
 8. The method of claim 7 wherein: determining the output capacity of the terminal unit includes sensing discharge air temperature of the terminal unit.
 9. A terminal unit system comprising: a controller; and a terminal unit having an actuator; the controller configured to control the actuator, the controller configured to perform operations comprising: detecting a stuck position of a first actuator in the terminal unit; receiving a command signal identifying a commanded capacity; and controlling a second actuator in the terminal unit in response to the stuck position of the first actuator and the commanded capacity.
 10. The terminal unit system of claim 9 wherein: controlling the second actuator comprises: accessing an adaptive coordination map, the adaptive coordination map associating the commanded capacity with a second actuator drive signal for the stuck position of the first actuator; and applying the second actuator drive signal to the second actuator.
 11. The terminal unit system of claim 9 wherein: controlling the second actuator comprises: computing a second actuator drive signal in response to the commanded capacity and the stuck position of the first actuator; and applying the second actuator drive signal to the second actuator.
 12. The terminal unit system of claim 9 wherein: the detecting the stuck position of the first actuator in the terminal unit includes providing a range of drive signals to the first actuator; and determining if the first actuator responds to the range of drive signals.
 13. The terminal unit system of claim 12 wherein: determining if the first actuator responds to the range of drive signals includes sensing movement of the first actuator.
 14. The method of claim 12 wherein: determining if the first actuator responds to the range of drive signals includes sensing fluid flow or temperature in the terminal unit.
 15. The method of claim 12 wherein: determining if the first actuator responds to the range of drive signals includes determining an output capacity of the terminal unit.
 16. The method of claim 15 wherein: determining the output capacity of the terminal unit includes sensing discharge air temperature of the terminal unit. 